In this study plasma membranes isolated from human diploid fibroblasts will be examined. The main objective is to correlate changes of fluidity and structural modifications in the membrane with age of the donor and with aging of cells in culture. In addition fibroblast membranes obtained from patients with Huntington's Disease, a genetically dominant disorder, will be studied with age-matched controls. The basic hypothesis is that structural changes occur within membranes during the aging process and in certain genetically dominant states. Properties of the isolated membrane preparations will be monitored by electron microscopic and biochemical techniques. Analysis of bound fluorescent probes will permit evaluation of changing patterns of protein-lipid interaction with aging and will lead to the development of a model of the human diploid fibroblast plasma membrane. This approach will be helpful in establishing the relationships of the plasma membrane to general aging processes within cells.